One Tailed Hypothesis

A one tailed hypothesis is used when you are interested in the determining the relationship between a sample and a distribution. In statistics you compare a sample (Example: one class of high school seniors SAT scores) and compare it to a larger set of numbers which is called a distribution (the SAT scores for all US high school seniors). One tailed tests look at whether the sample is greater OR less than the distribution but not both. This is where the name comes from: you are only interested in one side (known as a tail) of the distribution.

Using the SAT example, you are trying to determine if your high school class's SAT schools were the same as the US nationwide scores. You are only interested in knowing if your class's scores were higher than the national scores. Therefore you would form a one tailed hypothesis for your statistical test to determine if your scores were higher because you are only looking at one tail of the distribution.

See also: Two Tailed Hypothesis